The manufacturing of a container by blow molding consists ordinarily of inserting into a mold, constituting the impression of the container, a parison (it can be a preform or an intermediate container obtained by pre-blow-molding of a preform), previously heated to a temperature greater than the glass transition temperature of the material, and consists in injecting into the parison a fluid (particularly a gas such as air) under pressure. The blow molding can be completed by a preliminary stretching of the parison by means of a sliding rod.
The molecular dual orientation that the material undergoes during the blow molding (axial and radial, respectively parallel and perpendicular to the general axis of the container) imparts a certain structural rigidity to the container.
However, the requirements of the market economy, or the anti-pollution standards, lead manufacturers to use ever smaller amounts of material. Other things being equal, the effect of this is a reduction in the mechanical performance of the containers, due in particular to a reduced rigidity of the bottom that has a tendency to collapse under the hydrostatic pressure of the contents.
For this reason, a great deal of work has been done by the manufacturers on the shape of the bottoms to increase their rigidity.
Thus, it is known to make the bottom rigid by means of ribs; see, for example, French patent FR 2 753 435 (Sidel). This bottom keeps its mechanical strength without being inverted as long as the conditions of volume and/or pressure in the container are normal. However, when the conditions are extreme, the bottom nevertheless has a tendency to collapse.
In addition, arched bottoms, referred to as “champagne” bottoms, are known; see, for example, French patent FR 2 730 471 or its U.S. equivalent U.S. Pat. No. 6,153,145. This type of bottom, inspired by the bottoms of glass champagne bottles, exhibits the advantage of offering good strength as well as good stability, but it nevertheless has the drawback of using a large amount of material.
In practice, the most mechanically stable bottoms of containers are those whose shape comes closest to that of a sphere because of a distribution of relatively uniform stresses. However, a container with a spherical bottom cannot be stable if it is not for that matter provided with a base. This is why the majority of the containers with spherical bottoms (intended particularly for carbonated beverages), generally have added bases (particularly by snapping-on or by gluing, see, typically, U.S. Pat. No. 4,552,275 Owens Ill.) or formed by projecting from the bottom, see U.S. Pat. No. 5,122,325 Broadway Companies.
The added bases require additional operations for manufacturing and for reprocessing waste materials, which make this type of container undesirable in today's market. As for the bases formed by projection, they appear promising but produce manufacturing difficulties, to the point that, in U.S. Pat. No. 5,122,325 cited above, the base is already shaped on the preform from which the container is formed. This technique is not without drawbacks. First, it requires an addition of material. Then, the final formation of the base during the blow molding of the container is difficult to control.
Also, particularly for carbonated beverage applications, numerous petaloid-shaped bottoms are known, comprising an alternation of valleys, of hemispheric curvature, and of projecting feet, whose ends form a seat for the container; see, for example, French patent application FR 2 959 214 or its U.S. equivalent US 2013/043255. The petaloid-shaped bottom appears as a relatively successful solution combining good resistance to strong internal pressures in the container (because of the hemispheric curvature of the valleys) and a relative lightness. However, the petaloid-shaped bottom has the drawback of being rather unstable during operations of handling the container on the packaging lines.